Compounds of cobalt, iron, manganese, nickel and, more particularly, copper and zinc (hereinafter collectively referred to as “preservative metals”) are established preservatives for organic materials to prevent spoilage, decay and attack by pests. Such compounds, particularly those of copper, also have applications as agricultural and horticultural pesticides.
In order to apply the preservative metal compound to the porous materials in a manner suitable for it to act as a preservative, it is desirable to dissolve the compound in a carrier liquid which is capable of penetrating into the porous material.
Boron compounds in the form of boron oxide, boric acid and borate salts have a more recent history as wood preservatives, insecticides, fungicides and molluscicides replacing more toxic and environmentally undesirable materials such as chromates, arsenates, phenolic and organo-halogen pesticides, particularly poly-halogenated aromatic and cyclic compounds.
Boric acid (orthoboric acid and metaboric acid), borate salts, exemplified by borax (sodium tetraborate) and DOT (disodium octaborate tetrahydrate), are nowadays very widely used as they are effective, have low toxicity to higher life forms, have a small environmental impact at the concentrations normally used and are of relatively low cost.
To facilitate preservative activity against a wide range of spoilage organisms, it is advantageous to use more than one preservative agent. The blending of borates with one of the more usual salts of a preservative metal such as the sulfate, nitrate, chloride or acetate results in the formation of the insoluble borate salt of the preservative metal. Whilst these borate salts may have some of the desired enhanced preservative properties they are of very low solubility and are thus difficult to apply into the body of the substrate and thus have a limited action. There is thus a need for a method of combining the active borate ion and preservative metals whilst maintaining solubility in water and/or commonly used solvents.
In order to formulate useful combinations of preservative metals compatible with borate compounds, prior art has been mainly concerned with the formation and use of ammine and amine complexes of the preservative metals. These complexes have a number of disadvantages including a foul, often overpowering odor and toxicity. This has been partially overcome by the use of alkanolamines but these can introduce other problems. The release of odorous, potentially toxic vapors of ammine and amine complexes gives rise to unpleasant working conditions for operatives and requires the provision of extraction equipment or an enclosed working space. The release of ammonia and amines to the atmosphere on a large scale causes pollution and has an adverse effect on the environment.
There is thus a further need for water and glycol soluble preservative metal/borate combinations without the disadvantages described.